Telecommunication services have undergone tremendous advancement in the last decade. As an example, wireless or cellular telephone systems have now become largely ubiquitous. The advancement from analog cellular telephones, to more sophisticated digital telephones that utilize multiple access techniques such as CDMA or GSM has been very rapid.
Cellular digital telephone networks have been engineered primarily to carry voice communications, meaning the connections provided have a fixed maximum data rate, a low latency (as voice communication is sensitive to latency) and the connections can tolerate relatively high error rates (as voice communication can tolerate such error rates).
More recently, attempts have been made to offer data services (i:e. such as web-browsing) over existing cellular digital telephone networks, but in general these services are unacceptably slow, because such services have different requirements than voice communications. Specifically, while data services can accommodate relatively high latencies, they generally require low error rates.
Indeed, another example of recent advances in telecommunication services has been the deployment of IP protocol networks (such as the Internet and other networks), which have been primarily designed to transmit data. The Internet is an example of a network that is optimized for a relatively low error rate, but which is generally tolerant of latency. This optimization has lead to the result that the Internet is a poor medium for carrying voice services.
Recently, much has been written about “convergence”, wherein the next generation of telecommunication networks will be engineered to carry voice, data and other services. Such networks are expected to be ‘smart’, in that they will dynamically vary their prioritization of errors and delay, according to the quality-of-service (“QoS”) requirements of the service being carried over that network. Indeed, much hope was expressed for the so-called “3G” or third-generation of wireless phones, which were to offer good quality voice service and data services at high speeds and low error rates. To date however, the expectations of 3G have not been met, as the challenges of providing such networks have proven more greater than expected.
It is recognized, however, that the communication structures that will be required to deliver voice, data and other services at a appropriate QoS can be divided into two categories: delivering the service from the network to the subscriber, and delivering the service from the subscriber to the network. In wireless networks having a base station which communicates with a plurality of subscriber stations, the former category is typically known as the “downlink” and is a one-to-many link, and the latter category is known as the “uplink” and is a many-to-one link.
The 3G standard, available from a variety of sources including the web site of the Third Generation Partnership Project (3GPP) organization (www.3gpp.org) includes a channel structure that is intended to provide an uplink for voice, data and other services at a high QoS. The 3G channel structure includes a DDCH (dedicated data channel) which is intended to provide low latency connections for voice services in both the downlink and uplink directions by reserving transmission resources and a CPCH (common packet channel) which is intended to provide low error rate connections for bursty, latency tolerant, packet-based data on the uplink. In simple terms, the CPCH allows a plurality of subscriber stations to share an uplink to a base station by allowing them to randomly access that common channel. The CPCH is described in detail in the 3G documents and is also described in U.S. Pat. Nos. 6,169,759 and 6,301,286 to Kanterakis et al.
In a very simplified explanation, the subscriber stations served by the Kanterakis CPCH transmit a low power pre-defined sequence to the base station, the sequence representing a request by a subscriber station for permission to transmit on the CPCH at a future time. Once the sequence is transmitted, the subscriber station listens to a corresponding downlink channel from the base station for an authorization or denial to transmit. If the subscriber station does not receive either an authorization or denial from the base station, it will rebroadcast the request sequence to the base station at a higher power level, repeating the process until it receives a denial or authorization. If the subscriber station receives a denial of permission, it makes another request to the base station after a random delay. If the subscriber station receives an authorization, it sends a second request to the base station to confirm the authorization which reduces the chance that two different subscriber stations have made the same request at the same time. If it then receives a second authorization on the corresponding downlink channel, the subscriber station can commence transmitting on the CPCH at the appropriate time and power control information for the transmission on the CPCH is transmitted from the base station to the transmitting subscriber station on yet another channel designed for this purpose. Each of these circumstances and the operation of the CPCH is described in more detail in the above mentioned documents.
The inventors of the present invention have determined that, while the CPCH structure can provide low latencies and a reasonable bandwidth utilization efficiency at low utilization levels (i.e.—few users with little data to send), the performance and efficiency of the CPCH structure decreases significantly at higher utilization levels (i.e.—many users and/or large amounts of data to send). As will be apparent to those of skill in the art, as is the case with all random access techniques, as more subscriber stations attempt to access the CPCH, more collisions will result wherein two or more subscriber stations request permission to transmit at the same time. Because the mechanism for dealing with such collisions in the CPCH is to have the denied subscriber stations retry their request at random intervals, the mechanism quickly degrades to a very low level of efficiency when the number of subscriber stations increases and the latencies and bandwidth utilization efficiency can quickly reach unacceptable levels.
In the 3G system, the CPCH channels are typically over-provisioned in an attempt to mitigate this degradation. It is contemplated that bandwidth utilization efficiencies for the CPCH will not often surpass thirty percent of the maximum theoretical channel capacity.
Another technique for dealing with congested CPCH's is to transfer certain subscriber stations to DDCHs for their uplinks but, while this can result in good latency times, it results in poor utilization of radio resources as DDCH channels are not shared and are not radio resource efficient when transmitting bursty data.
In general, the inventors of the present invention believe that the CPCH can offer good performance for bursty data traffic at low levels of utilization, but is not suitable for higher levels of utilization.
It is therefore desired to provide a communication channel structure and method which makes efficient utilization of radio bandwidth and which is capable of providing low latency and/or low error rate communications.